1. Field of the Invention
The present invention generally relates to radio communications, and especially relates to a data-cache apparatus and a data-cache method that are used by a radio communications system.
2. Description of the Related Art
Service contents of radio communication systems are increasingly diversified with progress of system development, which trend will continue. Not only mere voice communication services, but services of distributing still images and motion pictures are being offered. Under this situation, in order to provide a higher quality service, various specifications based on the wideband CDMA method (W-CDMA method) are set forth by the 3GPP (3rd Generation Partnership Project) that is a standardization organization for the third generation mobile communications systems.
FIG. 1 is an overview of a radio communications system of this kind. The radio communications system includes mobile stations 102, base stations 104 that communicate with the mobile stations 102, radio network control units (RNC) 106 that are connected to the base stations 104, a packet switching apparatus 108 that is connected to the radio network control units 106, a gateway apparatus 110 that is connected to the packet switching apparatus 108, and Web servers 112 that are connected to the gateway apparatus 110.
An interface between the mobile stations 102 and the base stations 104 is expressed by Uu. An interface between the base stations 104 and the radio network control units 106 is expressed by Iub. An interface between the radio network control units 106 is expressed by Iur. An interface between the radio network control units 106 and the packet switching apparatus 108 is expressed by Iu.
FIG. 2 shows an example of a protocol stack of a cellular communication system such as described above. Therein, TCP expresses a Transmission Control Protocol, IP expresses Internet Protocol, and RLC expresses a layer of a Radio Link Control unit. MAC expresses a layer of Media Access Control. L1/L2 expresses a physical layer. FP expresses a layer of Frame Protocol. GTP-U expresses a GPRs Tunneling Protocol. USER expresses a process peculiar to a user performed on the user side.
When the mobile station 102 of FIG. 1 acquires data from a certain Web server 112 using a packet communication service, generally, the following process is performed. First, an RLC connection 202 for performing data transmission via a radio channel is set up. An RLC protocol is a protocol for ascertaining correctness of data in a radio transmission path, etc., and mainly deals with resending control, etc. The RLC protocol has three modes of operation, namely, a resend mode (AM: Acknowledge Mode), a non-resending mode (UM: Un-acknowledge Mode), and a transparent mode (TrM: Transparent Mode). When resending of data is actually performed, the resend mode (AM) is operated. Further, in the RLC protocol, for example, two or more logical channels are prepared to one protocol entity of one user, and the modes of operation can be individually assigned to each user by selecting the logical channels.
When an RLC connection is established between the mobile station 102 and the radio network control unit 106, a TCP/IP connection 204 is set up between the mobile station 102 and the Web server 112. In the TCP protocol, ascertaining the correctness of data such as a resending control is carried out as in the RLC protocol. Generally, the resending control of the TCP protocol handles a greater data size of data to resend, and is performed by a simpler process as compared with the radio resending control of the RLC protocol. When the TCP/IP connection is established between the mobile station 102 and the Web server 112, the radio network control unit 106 simply relays the data transmission between the mobile station 102 and the Web server 112. Under this situation, the mobile station 102 requests desired data of the Web server 112, and in response to the request, the Web server 112 provides the requested data.
The data request and distribution of the requested data are carried out by “USER” of FIG. 2. Specifically, it is common that it is carried out by HTTP (Hyper Text Transport Protocol) that operates on the TCP/IP. Further, while it is common to use HTML (Hyperlink Text Markup Language) as a description language, the language of cHTML (Compact HTML), WML (Wireless Markup Language), and others may be used.
Traffic of the data distribution service provided between the mobile stations and the Web servers will increasingly become great as the contents of service become diversified from now on, with an increase in the amount of data and an increase in the number of subscribers being added, and processing burden of the data distribution on the network side and service providers will become great. This will cause, for example, remarkable delays in data transmission. One method of solving this kind of problem can be to increase capacity of the Web server and others, preparing for the increased traffic. However, such new investment is a burden not only to the service providers, but also to the users since communication charges will have to be raised.
It is conceivable that the traffic burden of the network may be reduced if a data-cache function is provided to a relay node, since repetitive transmissions of the same data from the Web server to the mobile station can be avoided. However, no technology for providing the data-cache function to a radio communications system, such as 3GPP, has been reported. Data caching in systems other than 3GPP is disclosed, for example, by Patent Reference 1.
[Patent Reference 1] JPA, 2000-250803
If the conventional data cache is applied to the relay node such as the radio network control unit in an attempt to provide a data cache function to the radio communications system, there are problems. That is, since the radio network control unit only relays data as described above, all the data that pass through the radio network control unit will be stored by a cache memory. The data provided to the mobile stations include data that would not be requested again henceforth, like voice data and real-time data (for example, data provided by audio-video AV services). That is, data not suitable for temporary storage will be stored in large volume. With the added data control burden, such technique as above, i.e., applying the conventional method to the radio communication environment, does not provide a realistic solution.
Further, the data exchanged between the mobile station and the Web server can include confidential data, the secrecy of which should be protected, and such confidential data should not be indiscriminately stored and made available again. Although a method may be thought of wherein whether certain data are appropriate for caching is determined by kinds of language, such as HTML, the method remarkably reduces the convenience of the communication system and the flexibility of a design.